plant distribution around salt marshes in relation to soil acidity

Plant Distribution Around Salt Marshes in Relation to Soil AcidityAuthor(s): Edgar T. WherrySource: Ecology, Vol. 1, No. 1 (Jan., 1920), pp. 42-48Published by: Ecological Society of AmericaStable URL: http://www.jstor.org/stable/1929256 .

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PLANT DISTRIBUTION AROUND SALT MARSHES IN RELA- TION TO SOIL ACIDITY

EDGAR T. WHERRY

Washington, D. C.

It is often denied that soil acidity has any particular relation to the distribution of plants; but as far as can be determined from their writings the majority of those who hold this view have either never made any determinations of soil acidity whatever, or have based such measurements as they have made upon misleading methods or unsound views as to the nature of soil aciditv.1 As a result of many hundreds of determinations of soil acidity and alkalinity made by the recently described method2 upon plants growing under the widest possible range of physical and climatic conditions, the writer has found abundant evidence that the acidity of the soil is closely connected with the distribution of native plants. An account of a few ob- servations is presented here, to illustrate the possibilities of this method in throwing light on the significance of peculiar types of plant distribution.

When a plant is described as characteristic of acid or of alkaline soil, it is not intended to imply that this is the only factor of importance in determining the place of growth, nor that the acid or alkali acts directly upon the plant. Some plants may require, for themselves or for symbiotic organisms, a soil of a definite acidity (or alkalinity) ; others may be favorably affected by some physical or chemical property of the soil which accompanies the development of that acidity; and still others may be driven into soils of a certain degree of acidity by more vigorous species which monopolize neigh- boring soils of greater or less acidities. The measurement of the actual soil acidities and alkalinities connected with certain species of plants, which is all that is attempted here, is but one step in the working out of the problem of why a given plant grows in a certain place. It is hoped that the result.! presented will indicate, however, the considerable, if not fundamental, importance of this often neglected step.

One of the most remarkable features of the vegetation of southern New Jersey, as pointed out by Stone,3 is the presence of plants which are characteristic of the upland woods or meadows of the northern part of the State upon a strip of land extending southward along the coast, lying in part

I It is planned to discuss the last statement in a subsequent paper. 2 Journ. Wash. Acad. Sci., 10: 2I7. I920.

3 " The Plants of Southern New Jersey . . . " Ann Rept. N. J. State Mus. for ii0 88. i9iI.

42



PLANT DISTRIBUTION AROUND SALT MARSHES 43

between the pine-barrens and the salt-marshes, and in part between the latter and the ocean. A list of twenty typical species showing this distribution, selected from those given by Stone, follows :4

LIST I. PLANTS EXTENDING FROM NORTHERN UPLANDS SOUTH IN NEW JERSEY CHIEFLY

ALONG THE COASTAL AREA

Wood reed-grass ..................... (Cinina arundiniacea) Slender wild rye ...................... (Elymnus striatus) Low cyperus ...................... (Cyperus diandrus) Woolly sedge ...................... (Carex lanuginosa) Starry false solomon's seal ............. (Vagnera stellata) (Smilacina stellata) Wide-leaf ladies' tresses .............. (Ibidium plan tagineum) (Spiranthes lucida) American aspen ...................... (Populus treniuloides) Starry campion ...................... (Silene stellata) Spreading pearlwort .................. (Sagina procumbens) Blunt-leaf sandwort .................. (Arenaria (Moehringia) lateriflora) Columbine .. ...................... (Aquilegia canadensis) Lyre-leaf rock-cress .................. (Arabis lyrata) American burnet ...................... (San guisorba canadensis) Swamp wild rose ..................... (Rosa virginiana (lucida)) Hog peanut .......................,.(Falcata comosa) (Amphicarpa monoica) Herb Robert ...................... (Geranium (Robertiella) Robertianlum) Whorled milkwort .................... (Polygala verticillata) Shrubby bittersweet ................... (Celastrus scanidens) Northern bugle-weed ................. (Lycopus unziflorus) Pale wild sunflower ................... (Helianthus giganteus)

A few of the species of list I occur also in the marl area (Middle District) of southern New Jersey, but most of them are typical of the Pied- mont or even the Appalachian mountain provinces further to the northwest, and do not enter southern New Jersey except along the coastal area. Many of those in the list have been studied by the writer in one or the other of these regions, and their soils have proved to exhibit on the whole circumneutral reactions: the reaction may reach a specific acidity of IO or a similar specific alkalinity, but rarely lies farther than this from the neutral point.

More or less closely associated with these circumneutral soil species are found, in the coastal area, many plants which grow in southern New Jersey otherwise only in the pine-barren area, such as those in list 2.

LIST 2. PLANTS EXTENDING EASTWARD FROM THE PINE-BARRENS INTO THE NEW JERSEY

COASTAL AREA, BUT ABSENT FROM OTHER AREAS

Brake ........................ (Pteridium latiusculum) (Pteris aquilinum) Larger pine-barren club-moss .... (Lycopodium adpressum (Chapmanii) )

A The common names in this and the other lists are taken from Britton and Brown's "Illustrated Flora," with a few modifications; technical names are in accord- ance with the American code, but the synonymy is given in cases of recent changes which have not become generally accepted, and the names under the international code are likewise added.



44 EDGAR T. WHERRY

Pitch pine ................. (Pinus rigida) Panic grass ................. (Paniicum nxeridionale) Panic grass ................. (Paniicum oricola (variety of preceding?)) Panic grass ................. (Paniicum lucidum) Pine-barren cyperus ............ (Cyperus Torreyi) (Cyperus cylindricus) Twig-sedge ................. (Cladium (Mariscus) inariscoides) Grass-leaf rush ............... (Juncus aristulatus) Grass-pink orchid .............. (Liniodorum tuberosum) (Calopogon pulchellus) Early ladies' tresses ............. (Ibidium vernale) (Spiranthes vernalis) Southern wild flax ............... (Linurm (Cathartolinum) floridanum) Inkberry ............. .... (Ilex glabra) Shleep laurel ................. (Kalmia angustif olia) Stagger-bush ................. (Neopieris (Pieris) mariana) (Lyonia mariana) American cranberry ............ (Vaccinium (Oxycoccus) macrocarpon) White thoroughwort ............ (Eupatorium album) Blazing star ................. (Lacinaria grawinlifoclia var.) (Liatris graminifolia) Pine-barren goldenrod .......... (Solidago fistulosa) Bushy aster ................. (4stcr duniosus)

Tests of the soils supporting the above species in the pine-barrens have shown them to be practically throughout of the high specific acidity of 300.

The many writers on plant distribution who regard physical factors as dominant in determining the distribution of plants would find difficulty in explaining the occurrence of species normally found in fertile meadows or upon rock ledges, in the sterile shifting sands and damp depressions of this coastal area along with characteristic peat bog plants. It seemed worth while, therefore, to ascertain whether any light could be thrown on the matter by a study of the chemical features of the several soils concerned.

The soil of the salt-nmarshes is of course decidedly alkaline in reaction because of the calcium bicarbonate in the sea water; actual tests by the indi- cator method showed a specific alkalinity of about 3o. Hummocks extending above the water level show less alkalinity, but rarely reach neutrality.

At the contact of the marsh with the sands of the mainland or islands it

might be expected that the reaction would change gradually from alkalinity

to neutrality; for clean sand, made up of quartz and other practically in-

soluble minerals, of course is neutral. But such is not the case; the reaction

changes sharply, within the space of a few centimeters, from a specific alka-

linity of 30 to a specific acidity of 300; and the latter value is shown by the

sandy soils of the bogs, plains, and dunes to distances of hundreds of meters

back from the marsh margins.

The explanation of this change from alkalinity to acidity is not difficult

to find, if approached, not from the frequent viewpoint that soil acidity is a

high mysterious if not inscrutable phenomenon, but from a more modern

one. As pointed out in the writer's paper above cited, when a solution of

a neutral salt acts on a soil, both the clay and the humus present tend to

adsorb the basic element from the salt, and to set free the acid. When the




sea water is drawn up by capillarity, or distributed as spray by the wind to still greater distances from the shore, it yields to the soils some of its soda, and most of its lime and magnesia (compounds of bivalent elements being adsorbed more strongly than univalent ones), and as a result the soil acquires considerable acidity through the liberation of hydrochloric and sulfuric acids.5

It is accordingly possible to explain the occurrence in this coastal area of plants showing elsewhere widely divergent preferences as to habitat. The plants of list i evidently require in their soils an abundance of available lime and other bases, either free or in the form of salts, which requirement is here met; but they must be tolerant of high acidity. Those of the second list demand high acidity, which they find in the coastal area as well as in the pine-barrens; but they must be tolerant of the presence of salts. The other plants of neutral-soil upland regions, in so far as they have had an opportunity to migrate along the coast but have failed to do so, are pre- sumably to be interpreted as intolerant of acidity, even though adequately supplied with lime; and other plants of the pine-barren area, which have had a chance to extend coastward, but have not become established within the range of abundant spray, are no doubt to be classed as unable to withstand the presence of salts, in spite of the existence of a suitable degree of acidity.

There is of course no reason why such phenomena should be limited to New Jersey; and Professor M. L. Fernald has recently called the writer's attention to the fact that plants found elsewhere in fairly acid soils occur at the edges of salt marshes in Massachusetts under circumstances which have not heretofore been fully understood. These relations were studied espe- cially at the typical locality known as Oak Island, a few miles northeast of Boston.' This deposit of glacial debris in the midst of the salt marsh is occupied by a rich woods, with the typical upland flora shown in list 3 (list of species kindly furnished by Professor Fernald, common and American code names added by the writer).

LIST 3. PLANTS OF RICH WOODS, OAK ISLAND, MASSACHUSETTS

Slender wild rye .......... ... (Elymus striatus)7 Bottle-brush grass ............. (Hystrix patula (Hystrix)) Woolly sedge ....... ...... (Carex lanuginosa) 7

Canada lily .......... ....... (Lilium canadense) Trout lily ... ...... (Erythronium americanum) Bellwort ......... (Uvularia perfoliata) Showy orchid .... ..... (Orchis (Galeorchis) spectabilis)

5 The chemical substances are here referred to by the familiar terms lime, magnesia, hydrochloric acid, etc., although it is of course recognized that the phenomena observed are due directly to the ions; that is, lime is adsorbed as calcium-ion, a solution of hydrochloric acid reacts acid because of the free hydrogen-ion present, and so on.

,'WM. P. RICH, "Oak Island and its Flora." Rhodora, 4: 87. I902.



46 EDGAR T. WHERRY

Blunt-leaf sandwort ............... (Arenaria (Moehringia) lateriflora)7 Strong-scented meadow rue ......... (Thalictrum revolutum) 7

Red baneberry ..................... (Actaea rubra) Shrubby bittersweet ................ (Celastrus scandens) 7

Honewort ......... ........ (Deringa canadensis) (Cryptotacenia canadensis) Sweet cicely ............ ..... (Osmorrhiza (U/ashingtonia) longistylis) Fringed loosestrife ................ (Steironema ciliatunm) Richweed ................. (Collinsonia canadensis) Figwort ................. (Scrophularia marilandica) Wood betony ............... .. (Pedicularis canadensis) Lopseed ....... .......... (Phrymia Leptostachya) Horse gentian ................. (Triosteum aurantiacum) White rattlesnake root .............. (Prenanthes (Nabalus) alba)

The soil of this woods showed, when tested, a low degree of acidity, averaging a specific acidity of 3, the high content of lime and other bases in the glacial material from which the soil is derived evidently preventing the development of high acidity. The salt-marsh mud proved, as usual, to have a specific alkalinity ranging from 30 (wet portions) to as low as 3 (hummocks). Between the woods and the salt-marsh is a strip of damp ground a meter or two in width, supporting a flora quite unlike that of either woods or salt-marsh; instead, the species were found to be those elsewhere characteristic of peat bogs, sandy or peaty margins of ponds, sandy barrens, etc. A list of these (also by Professor Fernald, with common and Ameri- can code names added by the writer) follows in list 4; not all of the species are known to grow on Oak Island, but such as do not are found in quite similar places on the Massachusetts coast.

LIST 4. PLANTS OF UPPER BORDER OF SALT-MARSH, AT OAK ISLAND AND OTHER POINTS

ON MASSACHUSETTS COAST; USUALLY FOUND INLAND IN PEAT OR WET SAND, EXCEPT

AS NOTED.

Bog club-moss .............. (Lycopodiun inundatum) Switch grass ................ (Panicumn virgatunz) 8 (in damp sand) Blue-joint grass ............. (Calantagrostis canadensis) (also in swamps) Green spike-rush (sedge) ..... (Eleocharis olivacea)8 (also in wet bogs) Three-square sedge .......... (Scirpus anmericaius) 8 Twig-sedge .................. (Cladium (Mariscus) mariscoides)8 Canada rush ................. (Juilcus caniadensis)8 Turks-cap lily ............... (Liliumn superburn) Grass-pink orchid ............ (Lii aodorum tuberosum) (Calo pogon pulchellus)8 Pink bearded orchid .......... (Pogoniia ophioglossioides)8 Cross-leaf milkwort .......... (Polygala cruciata)8 Inkberry ................... (Ilex glabra) 8

Sweet pepper-bush ........... (Clethra alnifolia)8 Privet andromeda ............ (Xolisnia ligustrinia) (Lyaonia ligustrinla) (also in dry

barrens)

7 Found also in the coastal area of New Jersey.




Highbush blueberry .......... (Vaccinium corymbosum)8 (also in dry barrens) American cranberry .......... (Vacciniumn (Oxycoccus) inacrocarpon)8 Buckbean ................. (Menyanthes trifoliata) (also in wet bogs) Large gerardia ............... (Agaliniis (Gerardia) purpurea)8 Small gerardia ............... (Agalinis (Gerardia) paupercula) (also in dryish sands) Small bedstraw .............. (Galium trifidum) (also in wet bogs)

What a fine chance this was, we thought, for anyone who wished to deny the influence of acidity on plant distribution to get evidence apparently favorable to his view. No one could doubt that the salt-marsh muck is moderately alkaline, and everyone would be willing to admit that the rich woods soil might be slightly acid. The intervening strip of damp ground would naturally be inferred to be approximately neutral in reaction. Now, the vegetation of this strip is, as above noted, elsewhere characteristic of damp sandy or peaty places where the soil is admittedly highly acid. Clearly then, one might reason, these plants grow in both habitats because they find there the proper physical conditions, the optimum moisture content of the soil, for their best growth. Are they not, therefore, supremely indifferent to the fact that the acidity is several hundred times as great in the one habitat as in the other?

The tests of the reactions of the soils with the indicators spoiled this line of reasoning, however, by destroying the premise from which it started. The reaction of the intermediate strip, lying, it will be recalled, between a slightly acid soil on the one side and a moderately alkaline one on the other, proved to be nowhere near neutral in reaction; it was found to be instead strongly acid, specific acidity 300, just like the average sandy barren and peat bog. The reason for the development of this acidity at the border of the salt-marsh is of course the same as for that found in the New Jersey localities: the sea water is drawn up by capillarity into the soil around the edge of the woods, its bases are adsorbed by the clay and by the humus, and acids are set free. If the plants of list 4 really require high soil acidity, then. they can get it here as well as in any other of their habitats.

That the occurrence of the plants of list 4 in soils of acidity 300 is a matter of preference and not mere tolerance to high acidity is clearly indi- cated by the fact that the majority of these plants are not known to grow in any habitat of a much lower degree of acidity than this. In habitats such as stream banks and pond borders where the reaction is but weakly acid and no peat is forming, even though the water content of the soil is as near as may be to that in the places where they flourish, these plants are conspicuously absent. It can only be concluded from these relations that the majority of the plants in list 4 grow at the border of the salt-marsh and in wet sandy and peaty places because of the presence in both of these habitats of highly acid soils.

8 Found also in the coastal area of New Jersey.



48 EDGAR T. WHERRY

[Note.-Does not the acidity of the soil, which herein is shown to so strongly influence plant distribution, also influence the distribution of the animals living in the soil? Here is a problem for cooperation between the botanist, zoologist and chemist.

Progress in plant ecology has been seriously hampered by the theory that the important, if not the only soil factors influencing plant distribution, are the physical properties of the soil. Dr. Wherry's interesting paper should go far toward destroying this fallacy and stimulating soil research along chemical lines. Another paper by the same author explaining the cause of soil acidity and giving a simple field method for determining it will appear in ECOLOGY.-EDITOR. ]



plant distribution around salt marshes in relation to soil acidity

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